1. Field of the Invention
The present invention relates to clamp assemblies for securing a movable member to a column, and specifically to a clamp assembly for selectively clamping a movable cross-head to each column of a press having a plurality of columns.
2. Description of the Prior Art
In presses of many kinds it is necessary to secure a movable cross-head with respect to the columns of the press at one or more positions relative to the columns and the base of the press. For example, injection molding machines commonly comprise a two-part mold, and generally one half of this mold is mounted on a lower platen while the other half is mounted on an upper movable platen or cross-head to allow the mold to be opened and closed. Typically, one or more driving ram or cylinder assemblies is required for opening and closing the mold. Moldings are produced by injecting the material to be molded into the mold cavity under pressure. In the course of such injection, a force is built up which tends to separate the lower platen and cross-head to open the mold. In order to prevent this, it is necessary to firmly maintain the position of the lower platen with respect to the cross-head by a force at least as strong as the force created by the injected material. Rapid opening and closing of the mold is also desired in order to achieve economically advantageous production quantities.
Opposed hydraulic cylinders to force the lower platen and cross-head together is one method that has been tried to overcome the molding forces. Additionally, it has been common to devise means for clamping the cross-head in some fashion to the columns to limit its movement with respect thereto. For example, in United States Patent No. 4,304,540, granted to Hammon on Dec. 8, 1981, a hydraulic press is shown wherein the upper platen is secured vertically in position relative to the press columns by a plurality of wedge-shaped segments having teeth which engage a plurality of annular grooves on the column. The teeth of the segments are moved into engagement with the grooves of the column by a plurality of hydraulic cylinders which, when actuated, force the segments radially inwardly toward the columns. Similar column gripping arrangements are shown in the following British Patents:
______________________________________ British Pat. No. Grantee Publication Date ______________________________________ 803,553 Fabbrica Italiana 10/29/1958 Macchine Stampaggio ad Iniezione 1,512,449 Klockner-Werke 06/01/1978 Aktiengesellschaft 1,519,025 Klockner-Werke 07/26/1978 Aktiengesellschaft ______________________________________
Another method of clamping a member to a column is to position a U-shaped web about the column and exert pressure to urge the ends of the U together so that the web grips the column. Such a column gripping device is shown in U.S. patent application Ser. No. 493,651, filed May 11, 1983 on behalf of Martin M. Gram (a continuing application based on U.S. patent application Ser. No. 237,690, filed Feb. 24, 1981).